This invention relates to toner conveyors for electrostatographic processors and, more particularly, to methods and means for reclaiming the toner collected by the cleaning systems of such processors.
In a conventional electrostatographic printing process of the type described in Carlson's U.S. Pat. No. 2,297,691 on "Electrophotography", a uniformly charged imaging surface is selectively discharged in an image configuration to provide a latent electrostatic image which is then developed through the application of a finely divided coloring material, called "toner". As is known, that process has enjoyed outstanding commercial success, especially in plain paper xerographic copiers and duplicators. However, electrostatographic techniques are not limited to stand alone copiers and duplicator or even to xerography. For example, there are non-xerographic electrostatographic processors which have appropriately controlled stylii for selectively discharging the imaging surface to provide a latent image of the same general type as is generated by a xerographic processor. Furthermore, it has been found that xerographic and other electrostatographic processors have utility in a variety of arts, such as facsimile systems and computer printers, to name just a few.
Nevertheless, plain paper xerographic copiers and duplicators are generally representative of the problem to which this invention is addressed inasmuch as they rely on what is known as "transfer xerography". To automatically carry out that process, such a processor has a photosensitive imaging surface which is typically coated or otherwise deposited on a drum or belt which, in turn, is driven to sequentially advance the imaging surface through charging, exposure, development, transfer and cleaning stations.
The vehicle normally used to deliver the toner needed for development purposes is a multi-component developer comprising a mixture of toner particles and larger, so-called "carrier" particles. The materials for the toner and carrier (or, sometimes, carrier coating) components of the mixture are selected so that they are displaced from each other in the triboelectric series, whereby electrical charges of opposite polarities tend to be imparted to the toner and carrier particles when they rub together. Furthermore, in selecting the materials, consideration is given to their triboelectric ranking to the end that the polarity of the charge nominally imparted to the toner particles opposes the polarity of the latent images which are to be developed. Consequently, in operation, there are competing electrostatic forces acting on the toner particles. Specifically, there are forces which at least initially tend to attract them to the carrier particles. Additionally, the toner particles are subject to being electrostatically stripped from the carrier particles whenever they are brought into the immediate proximity of or actual contact with an imaging surface bearing a latent image.
Most of the toner deposited on the imaging surface during the development step is subsequently transferred to a suitable copy substrate (e.g., plain paper) as the imaging surface moves through the transfer station. Characteristically, however, there still is some residual toner which may be removed from the imaging surface before another copying cycle is initiated. To accomplish that, the cleaning station normally includes a blade, brush or some other means for dislodging the residual toner from the imaging surface and a sump for collecting that toner.
Others have already recognized that the practice of occassionally discarding the residual toner which collects in the sump of the cleaning system is a dirty and wasteful procedure. To overcome that problem, it has been suggested that a toner reclaim system be employed to transport the residual toner back into the development system where it can be re-used. That is a distinct improvement, but available toner reclaim systems are not altogether satisfactory.